In many types of rotating rigid disk files, each of the read/write transducers or heads is supported on a slider which rides on a cushion or bearing of air above the surface of the disk when the disk is rotating at its operating speed. The slider is connected to a linear or rotary voice coil actuator by means of a relatively fragile suspension. There is generally a stack of disks and a number of actuators with each actuator supporting a number of sliders. The actuators move the sliders radially between the disks so that each head may access the recording area of a respective disk.
In these conventional disk files the slider is biased against the disk surface by a small force from the suspension when the disk is not rotating. The slider is thus in contact with the disk surface from the time the disk file is turned on until the disk reaches a speed sufficient to cause the slider to ride on the air bearing. The slider is again in contact with the disk surface when the disk file is turned off and the rotational speed of the disk falls below that necessary to create the air bearing. In such disk files a lubricant is often maintained on the disk surface to prevent damage to the head and the disk during starting and stopping of the disk.
One type of disk for use in rigid disk files is a thin film metal alloy disk which typically comprises a substrate, such as an aluminum-magnesium (AlMg) alloy with a nickel-phosphorous (NiP) surface coating, a cobalt-based alloy sputter deposited as the magnetic layer on the substrate, and a protective overcoat, such as a sputter-deposited amorphous carbon film, formed on the magnetic layer. U.S. Pat. No. 4,503,125 describes a protective overcoat of amorphous carbon formed by sputtering a graphite target. Amorphous hydrogenated carbon films formed by reactive sputtering of a graphite target in an atmosphere of argon and hydrocarbon gases have been suggested as suitable for use as thin film disk protective overcoats, as described in Japanese Kokai No. 60-157725. Assignee's U.S. Pat. No. 4,778,582 describes a protective hydrogenated carbon overcoat formed by sputtering a graphite target in the presence of Ar and hydrogen (H.sub.2) In addition to the magnetic layer and the protective overcoat, thin film disks may also include a sputter-deposited underlayer, such as a layer of chromium (Cr), chromium-vanadium (CrV) or tungsten (W), between the substrate and the magnetic layer and a sputter deposited adhesion layer, such as a Cr, W or titanium (Ti) layer, between the magnetic layer and the protective overcoat.
A serious problem with such disk files is that after the slider has been in stationary contact with the disk surface (i.e. the protective overcoat) for just a short period of time, the slider tends to resist translational movement or "stick"to the disk surface. This "stiction" is caused by a variety of factors, including static friction and viscous shear forces and surface tension created by the lubricant between the disk and the slider. Even in those disk files which have disks with extremely smooth unlubricated disk surfaces, stiction may occur because of the strong intermolecular attraction at the interface between the smooth disk and slider surfaces. Stiction in a disk file can result in damage to the head or disk when the slider suddenly breaks free from the disk surface when disk rotation is initiated. In addition, because the suspension between the actuator and the slider is relatively fragile in order to permit the slider to fly above the disk surface, sudden rotation of the disk can also damage the suspension. The stiction problem is especially prevalent in those disk files which have amorphous carbon or hydrogen-containing carbon protective overcoats on the disks.
In order to prevent damage to the disk file caused by the stiction between the sliders and disk surfaces, various types of head load/unload mechanical and electro-mechanical devices have been built into disk files. A typical load/unload device thus moves the sliders away from the disk surfaces when the disk file is turned off and back towards the disk surfaces when the disk file is turned on. Thus, in contrast to conventional contact start/stop (CSS) disk files, in the "load/unload" type of disk files the sliders are never permitted to contact the disk surfaces.
In addition to the stiction problem, an additional problem in disk files which use thin film disks is the suitability of the protective overcoat to provide resistance to wear caused by contact of the disk by the air-bearing slider which carries the magnetic recording head.
Accordingly, it is desirable to have a protective overcoat for thin film metal alloy disks which is wear resistant and which presents a low static friction interface to the slider. With such an improved protective overcoat it is possible to have disk files which include all the advantages of both thin film metal alloy disks and CSS operation.